Application of the taraxerane–oleanane rearrangement to the synthesis of seco-oleanane triterpenoids from taraxerone

Synthetic oleananes and seco-oleananes form a group of promising anti-inflammatory and cancer chemopreventive agents with an excellent safety profile. These compounds are usually prepared by semi-synthesis from natural oleanane triterpenoids. Since a taraxer-14-ene was reported to be rearranged into an olean-12-ene under mild reaction conditions, a rapid synthesis of seco-oleananes from taraxerone, which is a readily available starting material, was explored by us. Treatment of taraxerone with m-chloroperoxybenzoic acid gave 14,15-epoxy lactones, which underwent the taraxerane–oleanane rearrangement leading to new seco-oleanane triterpenoids.     

New insights into the adsorption of 3-(trimethoxysilyl)propylmethacrylate on hydroxylated ZnO nanopowders

Functionalization of zinc oxide (ZnO) nano-objects by silane grafting is an attractive method to provide nanostructured materials with a variety of surface properties. Active hydroxyl groups on the oxide surface are one of the causes governing the interfacial bond strength in nanohybrid particles. Here, "as-prepared" and commercially available zinc oxide nanopowders with a wide range of surface hydroxyl density were functionalized by a well-known polymerizable silane coupling agent, i.e., 3-(trimethoxysilyl)propylmethacrylate (MPS). Fourier transform infrared (FTIR) and solid-state (13)C and (29)Si nuclear magnetic resonance (NMR) spectroscopic investigations demonstrated that the silane coupling agent was fully hydrolyzed and linked to the hydroxyl groups already present on the particle surface through covalent and hydrogen bonds. Due to a basic catalyzed condensation of MPS with water, a siloxane layer was shown to be anchored to the nanoparticles through mono- and tridentate structures. Quantitative investigations were performed by thermogravimetric (TGA) and elemental analyses. The amount of silane linked to ZnO particles was shown to be affected by the amount of isolated hydroxyl groups available to react on the particle surface. For as-prepared ZnO nanoparticles, the number of isolated and available hydroxyl groups per square nanometer was up to 3 times higher than the one found on commercially available ZnO nanoparticles, leading to higher amounts of polymerizable silane agent linked to the surface. The MPS molecules were shown to be mainly oriented perpendicular to the oxide surface for all the as-prepared ZnO nanoparticles, whereas a parallel orientation was found for the preheated commercially ZnO nanopowders. In addition, ZnO nanoparticles were shown to be hydrophobized by the MPS treatment with water contact angles higher than 60°.     

A modified multistage fatigue model to study the fatigue life of forged HS6-5-3 tool steel under high cycle fatigue

DIN type forged HS6-5-3 tool steel (AISI M3:2) is most commonly used in tooling industry and also in some engine parts. Those components are usually exposed to cyclic mechanical stresses and 90% of them failed by fatigue damage. For predicting the life time of this tool steel under high cycle fatigue (HCF) a modified multistage fatigue model found by McDowell is proposed, which leads to reduce effects and cost for predicting life time of this material. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

One new and several minor diarylheptanoids from Amomum muricarpum

A new natural diarylheptanoid, designated muricarpin, together with four diarylheptanoids were isolated from the rhizomes of Amomum muricarpum Elmer (Zingiberaceae) growing in Vietnam. Three known compounds, 1,7-bis(3,4-dihydroxyphenyl)heptan-3-yl acetate, 1-(4'-hydroxyphenyl)-7- (3″,4″-dihydroxyphenyl)heptan-3-yl acetate and 1-(3',4'-dihydroxyphenyl)-7-(4″-hydroxyphenyl)-heptan-3-one were isolated for the first time from the genus Amomum, meanwhile (5R)-5-hydroxy-1,7-bis(4-hydroxyphenyl)-heptan-3-one was found for the first time in plants. Their structures were determined using spectroscopic analyses.     

Solvent-free condensation of phenylacetonitrile and nonanenitrile with 4-methoxybenzaldehyde: optimization and mechanistic studies

The condensation of phenylacetonitrile with 4-methoxybenzaldehyde can be carried out by two solvent-free methods: i) using neat powdered KOH at room temperature with equivalent amounts of aldehyde, nitrile and base for 3 min, and ii) using K2CO3 in the presence of a phase transfer agent for 3 min under microwave activation or conventional heating. By extending the reaction time up to 10 min, four different products were obtained from phenyl or nitrile group migration. With nonanenitrile, only the second method could be applied to give two kinds of condensed compounds with or without phenyl (or nitrile) group migration. The intervention of non-thermal MW-specific effects was proved in some cases and interpreted.     

A new diarylheptanoid and a rare dammarane triterpenoid from <Emphasis Type="Italic">Alnus nepalensis</Emphasis>

A new diarylheptanoid, a rare dammarane triterpenoid, and centrolobol were isolated from the leaves of Alnus nepalensis D. Don (Betulaceae). Their structures were determined by using spectroscopic analysis.     

Multivariate calibration combined differential pulse voltammetry for simultaneous electroanalytical determination of phenolic compounds using a Fe3O4-modified carbon paste electrode

Journal of Solid State Electrochemistry - In present study, a simple carbon paste electrode modified with iron oxide nanoparticles was used as an electrochemical sensor to analyze phenolic...